The invention relates to a device having touch sensitivity functionality comprising a surface and touch-sensitive means for detecting the presence of a touch input member being in contact with or close to the surface generating a distance sensor signal. The invention further relates to a touch sensitivity display device, to a keyboard and to a method of sensing a touch of a touch sensitivity device by a touch input member in such a device.
High resolving LCD screens enter more applications such as mobile phones and portable control devices. Touch screen functionality of these screens is desired in most of these applications. To determine where a display screen is touched, capacitive and resistive touch-sensitive layers are commonly used. They are based on transparent conductors such as indium-tin oxide films. Their disadvantage is the limited transparency which reduces the picture quality, particularly of modern high resolving LCD displays.
Another concept of detecting the presence of a touch input member being in contact with the display screen is based on an orthogonal array of paired light emitters and detectors for covering the display surface with crossed light beams and scanning means coupled to the emitters and detectors for electronically scanning the orthogonal arrays such that a single emitter at any one time is emitting light. Such a display device is, for instance, described in U.S. Pat. No. 4,301,447.
It is therefore the object of the present invention to provide a device having touch sensitivity functionality which does not require to add a layer to the surface, e.g. to the display screen, reduces the picture quality and does not further require a plurality of light emitters and detectors and complex control and image processing means. Particularly, a cheap and reliable solution is required.
This object is achieved by a device which is characterized in that that the touch-sensitive means comprises means for emitting a laser beam in a plane parallel and close to the surface, said laser beam being periodically deflected across the entire surface, and means for receiving the light reflected or scattered from the touch input member generating said distance sensor signal therefrom.
The invention is based on the idea of using distance measurement by means of a laser. The simple and cheap method of measuring a distance using a laser beam is generally known. This method shall be applied to a device in order to provide a touch sensitivity, thus avoiding an additional layer or arrays of light emitters and detectors as well as complex control and processing means.
According to the invention, a laser beam is emitted by a laser-emitting and detecting means such that it periodically scans the entire surface. If no such input member is in contact with the display screen or at least so close to the surface that it is hit by the laser beam, which touch input member may be, for instance, an electronic pen, a pointer or a user""s finger, the laser beam is reflected or scattered from the frame of the surface into the laser detector or there is no laser beam reflected. If a touch input member is in contact with the surface or at least so close to the surface that it is hit by the laser beam, the laser beam is reflected or scattered from the touch input member into the laser detector. The distance sensor signal generated by a laser detector will then show a significant change and, will allow determination of the position of the touch input member on the surface. Since an optical principle is used according to the invention, the solution is highly reliable and precise.
Preferred embodiments of the invention are defined in the dependent claims. Preferably, the position of the touch input member is calculated from the angle of emission of the laser beam and from the distance between the laser-emitting and detecting means and the direction of reflection, which distance is included in or can be derived from the light received by the laser detector. Particularly, in the phase of the light received by the laser detector as a function of the varying laser emission wavelength, information about the length of the way the laser light has gone from the laser-emitting and detecting means to the laser detector is included.
Preferably, the touch-sensitive means comprises a laser diode and a photo diode. Advantageously the laser diode is commonly used for emitting and detecting the laser beam. The light emitted from the laser diode is scattered back into the laser diode, thus modulating the emitted laser beam.
Furthermore, the laser-emitting and detecting means and the laser detector are preferably positioned within the frame of the display screen, particularly in the same corner of the frame. Thus, the invention can be easily used for any screen size and type which is important for mass production.
According to a preferred embodiment, the frame of the surface is not used to scatter the light and generate a distance reading. Only if a touch input member is in contact with the surface or is at least so close to the screen that it is hit by the laser beam, the laser beam is reflected or scattered from the touch input member into the laser detector. If no touch input member is present, no distance reading is generated.
Alternatively, laser reflection means, e.g. reflecting surfaces, can be put at certain positions on the frame, preferably in one or more corners so that the position of the beam and/or the surface size can be calibrated. Basically, such laser reflection means may simply comprise a white frame sufficiently reflecting and/or scattering the laser beam. In this wayxe2x80x94if no touch input member is presentxe2x80x94the distance between the laser-emitting and detecting means and the frame is continuously measured. When a touch input member is present, before hitting the touch input member and after hitting the touch input member, the distance to the frame is measured. This information can be used to calibrate the angle of the laser beam while hitting the touch input member. In the time when hitting the touch input member with the laser beam, the distance between the touch input member and the sensor is measured. The resulting information about angle and distance can be used to determine the coordinate where the screen is touched.
The laser-emitting and detecting means are preferably positioned for emitting the laser beam in a plane directly above the display screen. Thus it is quite easy to detect if a touch input member comes in contact with the surface or even if it is already very close to the surface. Alternatively, the laser-emitting and detecting means could also be positioned slightly below the surface or a layer above the surface such that the laser beam is emitted in a plane directly under the surface or said layer. In order to detect if a touch input member is in contact with the surface or said layer, it is necessary that the surface or said layer is flexible and that the touch input member generates a depression in the surface or said layer such that the laser beam is reflected from this depression instead of from the frame of the surface.
According to a preferred embodiment, distance measurement based on laser selfmixing is used. Therefore a laser diode is commonly used as laser-emitting and detecting means and as laser detector and the light emitted from the laser diode is scattered back into the laser diode thus modulating the generated laser beam. These modulationsxe2x80x94commonly also called xe2x80x9cundulationsxe2x80x9dxe2x80x94are detected by monitoring the laser output power with a detecting means, commonly a photodiode. If the laser diode itself is current-modulated, this effect can be used to measure the distance between the laser diode and the target, i.e. between the laser diode and the frame reflecting the laser beam or the contact point of the touch input member reflecting the laser beam. The simple and cheap method of measuring distances based on laser selfmixing is known in general, but can be favourably applied to a display screen to implement touch sensitivity functionality.
For deflecting the laser beam periodically across the entire display screen, oscillating means are preferably provided which periodically change the orientation of a mirror for deflecting the laser beam. Preferably, said oscillating means comprises an electronically driven mechanical oscillator such as is known from simple battery-powered mechanical alarm clocks or watches. However, other implementations of oscillating means are also possible.